substation transformer 1

[vanskat]

I have a 2500kVA Liquid Insulated (13.8kV/480V Y) substation transformer that has been accidentally hit by a pipe being lifted by a crane. Approx 10 of the radiator fins have been damaged!

Preliminary tests do not show any serious restriction in oil flow or any elevated temperatures.

Are there any suggestions to other tests that can be performed online.....

 

[RRaghunath]

Vanskat,

Thermography (infrared scanning) could reveal localised overheating, if any.

 

[vanskat]

Thanks

Our thermo scans did not reveal any anomalies in thermal distribution profile nor did our leak detector reveal any bad news. Is this enough to go on in making a conclusion?

 

[peebee]

I'd ask the manufacturer to take a look. Sounds like it's probably OK, but keep your fingers crossed. . . .

 

[busbar]

If the tank carries any pressure rating, a qualified person should determine whether or not the rating has been compromised by the damage. Also, did the collision affect any insulation or conductor properties?

 

[RajT]

Since there are no obvious changes in operating parameters, I would not worry about it.

 

[xfmr]

If you are seriously concerned, you could do a full-load heat run. Load the unit (with resistor banks, if necessary) to 2500 kva and run until oil and winding temperatures stabilize for at least 30 minutes. If you can do this without exceeding the design temperature limits for oil and winding, the transformer is fully operational.

However, under normal circumstances, I'd agree with RajT. Most people don't run that size transformer anywhere near full load, so there's usually excess cooling capacity available. Unless this is a system-critical unit, a heat run is probably not worth the effort.

 

[vanskat]

Thanks for all suggestions. Tfr has been given a clean bill of health after numerous tests. Was trying to be proactive with activities in order to avoid damage/failure etc

 

[electricpete]

So it appears the transformer is fit to continue service. Now you wonder about what to do with the long-term.

I agree it sounds like any reduction in thermal performance isn't a big concern. If there was any significant reduction, you will be alerted to this condition by temperature alarms or readings.

I would think the one serious long-term concern you have is whether a radiator fin is going to crack wide open after many thermal cycles several years from now. That can have some serious consequences. I have seen it happen.... although there was no prior known damage to the radiator... it split open one day when the transformer was rapidly heating up (nitrogen system provides makeup to counteract for contraction but does not compensate for expansion). At somewhere around 8 pounds it let loose. Relief was 10 pounds. Manufacturer said it was one of those things that never happened to anybody else....

I would think that in the short term you want to make sure it has a good rust-preventative coating to protect the areas that have been damaged. In the long-term you may want to think about replacing that radiator or removing it for careful inspection/repair. Depending on the overall thermal picture you might prefer to isolate the damaged radiator using installed valves or perform some kind of weld repair to isolate the damaged section.

 

[vanskat]

Pete,
I was battling with the same concerns.

I was thinking of adding a Nitrogen blanket (pressuring the tank to say +ve 4 psi (manufact specs) and see if this falls off. My main fear was that since this tfr has been in service for 35 years (up to 70% loading), I might actually create a leak by pressuring the tank.

Currently, the tfr looks a bit shaky (rusting etc) and it is about time we start looking to a replacement. This cant be done until the next 3 months but in the interim I want to get the best perfromance possible from the unit.

After 35 years I guess there is no real "long term"

Thanks

 

[jbartos]

Suggestion: Have a material science specialist to assess the radiator material damages. Then, follow the material scientist's recommendations.